The difference this year is that Romney's share of the Hispanic vote is lower than McCain's and that the Hispanic share of the voting population is growing. But the growth has been gradual, not abrupt. Hispanics made up 10% of the electorate in 2012, compared with 9% in 2008 and 8% in 2004. The Hispanic vote helped the president, but was not the decisive element.
Some point to the 2004 election to suggest that the GOP has seen a dramatic dropoff in Hispanic support. But careful analysis suggests that 2004 exit polls overstated Bush's showing among Hispanic voters.
Here are the exit poll figures. The 1976 poll lacks data for Hispanics. The 1992 and 1996 figures for both parties are lower because of the Perot vote.
Sources: New York Times and CNN